Many catheter-based endovascular interventional procedures have become common. For example, angioplasty and stenting are used to treat cardiac, peripheral and neurovascular disease. Stent-grafting is used to treat thoracic and abdominal aortic aneurysms. Also, endovascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. Typically, in embolization procedures intended to treat cerebral aneurysms, platinum coils are used to occlude vascular structures throughout the body, including vascular aneurysms.
Vascular aneurysms are produced when a thinning or weak region in a vessel wall dilates, eventually posing a health risk from its potential to rupture. While aneurysms can occur in any blood vessel, most occur in the aorta and cerebral arteries. The etiology of aneurysm formation is not entirely understood, but is thought to be related to effects of fluid dynamics, atherosclerotic vessel degeneration, vessel trauma, infection, smoking, high blood pressure, and other causes leading to vessel degeneration. Left untreated, aneurysms may lead to gradual vessel expansion, thrombus formation leading to stroke or other vessel blockage, vessel rupture, shock, and eventual death.
Several different treatment modalities have been employed in the endovascular occlusion of vascular aneurysms. For example, U.S. Pat. No. 4,819,637 to Dormandy, Jr. et al., the entire disclosure of which is incorporated herein by this reference, describes a vascular embolization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter and is inflated inside the aneurysm with a solidifying fluid (typically a polymerizable resin or gel) to occlude the aneurysm. The balloon is then detached from the catheter by gentle traction on the catheter. While the balloon-type embolization device, such as described in Dormandy, Jr. et al, can provide an effective occlusion of many types of aneurysms, the device can be difficult to retrieve or move after the solidifying fluid has set. In addition, the device is difficult to visualize. Furthermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon from the catheter.
In recent years, detachable platinum coils have become widely used to treat cerebrovascular structures such as aneurysms, fistulae, arterio-venous malformations, and vessels. Platinum coils induce blood stasis and thrombus formation in the vascular structure. In some structures, the platinum coils achieve the desired patient outcomes. For example, in small aneurysms with small necks, platinum coils are extremely efficacious. However, in aneurysms that are large, wide-necked, or fusiform, the outcomes of platinum coils are not optimal. In particular, some of these devices, for example, such as devices disclosed in Guglielmi, et al., U.S. Pat. No. 5,122,136, the entire disclosure of which is incorporated herein by this reference, have a secondary configuration such as a helix or some similar form. These devices form a three-dimensional non-minimum energy state configuration when deployed inside an aneurysm; however, they have displayed a tendency to revert to their minimum energy state configurations over time. This, in turn, results in compaction due to “coin stacking” (i.e., returning to the secondary helical configuration), thereby allowing recanalization of the aneurysm.
A further development has been described in Greene et al., U.S. Pat. No. 6,602,261, the entire disclosure of which is incorporated herein by this reference. Greene et al. describe an embolization device that includes one or more expansible, hydrophilic embolizing elements non-releasably carried along the length of a filamentous carrier.
Another approach is the direct injection of a liquid polymer embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, and then is polymerized in situ. Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer mixed with bismuth trioxide and dissolved in dimethyl sulfoxide (DMSO). Another type is ethylene vinyl alcohol dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this “direct injection” method are disclosed in U.S. Pat. No. 4,551,132 to Pasztor et al.; U.S. Pat. No. 4,795,741 to Leshchiner et al.; U.S. Pat. No. 5,525,334 to Ito et al.; and U.S. Pat. No. 5,580,568 to Greff et al. The disclosure of each document cited herein is incorporated herein in its entirety by this reference.
Despite these advances in the capabilities of embolization materials, more effective methods of treating a defect in a vascular structure are needed, wherein the methods can be easily accomplished using a catheter, for example a microcatheter, have reduced risk of emboli, and allow formation of a structure amenable to physiological healing responses. The present invention provides such methods and systems or kits for performing such methods, the methods and systems being useable in various applications, including, but not limited to, medical implant applications wherein the material is used as or in conjunction with aneurysms, fistulae, arterio-venous malformations, vessel occlusions, and other vascular structures.